Method and apparatus for video coding

ABSTRACT

Aspects of the disclosure provide methods and a decoder device for video decoding. In some embodiments, the decoder device for video decoding includes processing circuitry. The processing circuitry selects a motion vector of a neighboring sub-block that is a neighbor of a current block under reconstruction. The current block is in a coded picture that is a part of a coded video bitstream. The processing circuitry determines, from the motion vector, motion vector predictors for a plurality of sub-blocks included in the current block. The neighboring sub-block and the plurality of sub-blocks are in a first one of a single row and a single column of the coded picture.

INCORPORATION BY REFERENCE

This application claims the benefit of priority from U. S. ProvisionalApplication No. 62/595,939, filed on Dec. 7, 2017, which is herebyincorporated by reference herein in its entirety.

TECHNICAL FIELD

The disclosed subject matter relates to video coding and decoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding using inter-picture prediction with motioncompensation has been known for decades. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GByte of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce aforementioned bandwidth or storage space requirements,in some cases by two orders of magnitude or more. Both lossless andlossy compression, as well as a combination thereof can be employed.Lossless compression refers to techniques where an exact copy of theoriginal signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between theoriginal and reconstructed signal is small enough to make thereconstructed signal useful for the intended application. In the case ofvideo, lossy compression is widely employed. The amount of distortiontolerated depends on the application; for example, users of certainconsumer streaming applications may tolerate higher distortion thanusers of television contribution applications. The compression ratioachievable can reflect that: higher allowable/tolerable distortion canyield higher compression ratios.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived fromneighboring area's MVs. That results in the MV found for a given area tobe similar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described here is atechnique henceforth referred to as “spatial merge”.

Referring to FIG. 1, a current block (101) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bedirected from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (102 through 106, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and a decoder device for videodecoding. In some embodiments, the decoder device for video decodingincludes processing circuitry. The processing circuitry selects a motionvector of a neighboring sub-block that is a neighbor of a current blockunder reconstruction. The current block is in a coded picture that is apart of a coded video bitstream. The processing circuitry determines,from the motion vector, motion vector predictors for a plurality ofsub-blocks included in the current block. The neighboring sub-block andthe plurality of sub-blocks are in a first one of a single row and asingle column of the coded picture.

In an embodiment, the neighboring sub-block and the plurality ofsub-blocks are in the single column of the coded picture, and theneighboring sub-block is a top neighbor above the plurality ofsub-blocks.

In an embodiment, the neighboring sub-block and the plurality ofsub-blocks are in the single row of the coded picture, and theneighboring sub-block is a left neighbor of the plurality of sub-blocks.

In an embodiment, a motion vector predictor for each remaining sub-blockincluded in the current block is determined from a motion vector of aneighboring sub-block that is a neighbor of the current block andincluded in one of a single row and a single column with the respectiveremaining sub-block that is parallel to the first one of the single rowand the single column.

In an example, the processing circuitry decodes a codeword from thecoded video bitstream. The codeword indicates the first one of thesingle row and the single column.

In an embodiment, the processing circuitry decodes, from the coded videobitstream, a residual motion vector for one of the plurality ofsub-blocks. The processing circuitry combines the motion vectorpredictor for the one of the plurality of sub-blocks with the residualmotion vector to derive a motion vector for the one of the plurality ofsub-blocks. In an example, the derived motion vector is used todetermine motion vectors for the remaining sub-blocks of the pluralityof sub-blocks.

In an example, the processing circuitry decodes at least one syntaxelement from the coded video bitstream. The at least one syntax elementindicates the first one of the single row and the single column.

In an example, the processing circuitry determines motion vectors forthe plurality of sub-blocks based on the motion vector predictors andusing one of: template matching and bilateral matching.

In an example, the processing circuitry selects another motion vector ofanother neighboring sub-block that is a neighbor of the current block.The processing circuitry determines, from the other motion vector,another motion vector predictor for one of the plurality of sub-blocks.The other neighboring sub-block and the one of the plurality ofsub-blocks are in a second one of a single row and a single column ofthe coded picture. The second one of the single row and the singlecolumn is perpendicular to the first one of the single row and thesingle column. The processing circuitry determines a motion vector forthe one of the plurality of sub-blocks based on the motion vectorpredictor and the other motion vector predictor of the one of theplurality of sub-blocks. In an example, the processing circuitrydetermines the motion vector for the one of the plurality of sub-blocksusing a weighted combination of the motion vector predictor and theother motion vector predictor for the one of the plurality ofsub-blocks.

Aspects of the disclosure also provide a non-transitorycomputer-readable storage medium storing a program executable by atleast one processor for video decoding to perform any of the methods forvideo coding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a current block and itssurrounding spatial merge candidates in accordance with H.265.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 6 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 7 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 8 is a schematic illustration of a motion vector prediction of ablock and sub-blocks used for, or affected by, motion vector prediction.

FIG. 9 is a schematic illustration of a vertical motion vectorprediction with uniform and square sub-block dimensions.

FIG. 10 is a schematic illustration of a vertical motion vectorprediction with rectangular and non-uniform sub-block sizes.

FIG. 11 is a schematic illustration of a horizontal motion vectorprediction with uniform and square sub-block dimensions.

FIG. 12A is a schematic illustration of a diagonal motion vectorprediction with uniform and square sub-block dimensions.

FIG. 12B is a schematic illustration of a diagonal motion vectorprediction with non-uniform sub-block dimensions.

FIG. 13 is a schematic illustration of a top-right diagonal motionvector prediction with uniform and square sub-block dimensions.

FIG. 14 is a schematic illustration of a bottom-up diagonal motionvector prediction with uniform and square sub-block dimensions.

FIG. 15 is a schematic illustration of a motion vector prediction with aprediction direction 1501.

FIG. 16 is a schematic illustration of a motion vector prediction with anon-integer location.

FIG. 17 shows a flow chart outlining a process (1700) according to someembodiments of the disclosure.

FIG. 18 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure are directed to reducingredundancy in motion vector coding.

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. Thecommunication system (200) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (250). Forexample, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210) for transmissionto the other terminal device (220) via the network (250). The encodedvideo data can be transmitted in the form of one or more coded videobitstreams. The terminal device (220) may receive the coded video datafrom the network (250), decode the coded video data to recover the videopictures and display video pictures according to the recovered videodata. Unidirectional data transmission may be common in media servingapplications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (250) represents any number ofnetworks that convey coded video data among the terminal devices (210),(220), (230) and (240), including for example wireline (wired) and/orwireless communication networks. The communication network (250) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(250) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (313), that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304) (or coded video bitstreams), can be processedby an electronic device (320) that includes a video encoder (303)coupled to the video source (301). The video encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (304) (or encoded video bitstream (304)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (302), can be stored on a streamingserver (305) for future use. One or more streaming client subsystems,such as client subsystems (306) and (308) in FIG. 3 can access thestreaming server (305) to retrieve copies (307) and (309) of the encodedvideo data (304). A client subsystem (306) can include a video decoder(310), for example, in an electronic device (330). The video decoder(310) decodes the incoming copy (307) of the encoded video data andcreates an outgoing stream of video pictures (311) that can be renderedon a display (312) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Codingor VVC. The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle playouttiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412) (e.g., a display screen) that is not an integralpart of the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. 4. The control information for therendering device(s) may be in the form of Supplementary EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (420) may perform entropy decoding/parsing operation on thevideo sequence received from the buffer memory (415), so as to createsymbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks comprising sample values, thatcan be input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (452) has generated to the outputsample information as provided by the scaler/inverse transform unit(451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (453) in the form of symbols (421) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (457) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as document in thevideo compression technology or standard. Specifically, a profile canselect a certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example mega samples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540) (e.g., transmitting circuitry). The videoencoder (503) can be used in the place of the video encoder (303) in theFIG. 3 example.

The video encoder (503) may receive video samples from a video source(501)(that is not part of the electronic device (520) in the FIG. 5example) that may capture video image(s) to be coded by the videoencoder (503). In another example, the video source (501) is a part ofthe electronic device (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any color space (for example, BT.601 Y CrCB, RGB, . . . )and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focusses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (550) can be configured to have other suitablefunctions that pertain to the video encoder (503) optimized for acertain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4. Brieflyreferring also to FIG. 4, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415), andparser (420) may not be fully implemented in the local decoder (533).

An observation that can be made at this point is that any decodertechnology except, for example, the parsing/entropy decoding that ispresent in a decoder also necessarily needs to be present, insubstantially identical functional form, in a corresponding encoder. Forthis reason, the disclosed subject matter focuses on decoder operation.The description of encoder technologies can be abbreviated as they arethe inverse of the comprehensively described decoder technologies. Onlyin certain areas a more detail description is required and providedbelow.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies known to a person skilled in the art as, for exampleHuffman coding, variable length coding, arithmetic coding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of Intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A Predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A Bi-directionally Predictive Picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference pictures. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, Supplementary EnhancementInformation (SEI) messages, Visual Usability Information (VUI) parameterset fragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to Intra prediction) makes uses of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first and a second reference picture thatare both prior in decoding order to the current picture in the video(but may be in the past and future, respectively, in display order) areused. A block in the current picture can be coded by a first motionvector that points to a first reference block in the first referencepicture, and a second motion vector that points to a second referenceblock in the second reference picture. The block can be predicted by acombination of the first reference block and the second reference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency. In various embodiments, in themerge mode, a block in the current picture can inherit motion vectors ofa neighboring block (e.g., that shares a boundary with the block, isdisposed in a larger partition region with the block) in the currentpicture.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (603) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621) and anentropy encoder (625) coupled together as shown in FIG. 6.

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform and, in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques).

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intra,the general controller (621) controls the switch (626) to select theintra mode result for use by the residue calculator (623), and controlsthe entropy encoder (625) to select the intra prediction information andinclude the intra prediction information in the bitstream; and when themode is the inter mode, the general controller (621) controls the switch(626) to select the inter prediction result for use by the residuecalculator (623), and controls the entropy encoder (625) to select theinter prediction information and include the inter predictioninformation in the bitstream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) or the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata in the frequency domain, and generate the transform coefficients.The transform coefficients are then subject to quantization processingto obtain quantized transform coefficients.

The entropy encoder (625) is configured to format the bitstream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard, such asHEVC standard. In an example, the entropy encoder (625) is configured toinclude the general control data, the selected prediction information(e.g., intra prediction information or inter prediction information),the residue information, and other suitable information in thebitstream. Note that, according to the disclosed subject matter, whencoding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 7 shows a diagram of a video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive a coded pictures that are part of a coded video sequence, anddecode the coded picture to generate a reconstructed picture. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7.

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example,intra, inter, b-predicted, the latter two in merge submode or anothersubmode), prediction information (such as, for example, intra predictioninformation or inter prediction information) that can identify certainsample or metadata that is used for prediction by the intra decoder(772) or the inter decoder (780) respectively residual information inthe form of, for example, quantized transform coefficients, and thelike. In an example, when the prediction mode is inter or bi-predictedmode, the inter prediction information is provided to the inter decoder(780); and when the prediction type is the intra prediction type, theintra prediction information is provided to the intra decoder (772). Theresidual information can be subject to inverse quantization and isprovided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information (to include the QuantizerParameter QP), and that information may be provided by the entropydecoder (771) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503) and (603), and thevideo decoders (310), (410) and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503)and (603), and the video decoders (310), (410) and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503) and (503), and the videodecoders (310), (410) and (710) can be implemented using one or moreprocessors that execute software instructions.

Described below is the operation of the motion vector predictionaccording to the disclosed subject matter.

In general, motion compensation refers to techniques where one or moremotion vectors (MVs) are used to indicate a displacement of a sample oran area of samples relative to a position of the sample or the area ofsamples in a reference picture. In order to simplify the description,henceforth, the areas of samples are assumed to be of rectangular shapeand are referred to as “a block” or “a sub-block”, depending on context.The disclosure is applicable to and can be adapted accordingly for areasthat are not rectangular shaped.

In some embodiments, MVs of a block to be motion compensated can bepredicted from one or more blocks that are coded, i.e., encoded/decoded.In some embodiments, two modes of MV prediction can be used, and the twomodes include a merge mode and a residual mode. The merge mode, as usedherein, refers to MV predictions using one or more MV predictors (suchas, MVs associated with surrounding or neighboring samples of the block)without the use of a residual MV. Which of the MVs, in what combination,and with what weighting among the MVs are used can, in some examples, becoded as additional (or side) information. In other examples, theadditional information may be predictable, and, therefore, may not needto be explicitly coded. The residual mode (or regular mode) refers tothe use of a residual MV that is also coded in addition to the sideinformation. For example, in the residual mode, a MV of a current blockcan be obtained by adding a MV predictor of the current block and aresidual MV of the current block. As described above, the sideinformation may or may not be coded. In some embodiments, in a samevideo picture coded in accordance with a given video coding technology,both the merge mode and the residual mode are employed.

Embodiments of the present disclosure can be used in the merge mode, theresidual mode, or a combination thereof. The description below uses themerge mode as an example unless noted otherwise for purposes of clarity.

In general, the techniques for MV predictions described herein can beimplemented in, or be part of, a video encoder (also referred to as anencoder) or a video decoder (also referred to as a decoder). Asdescribed above, encoders and decoders can implement similar techniques,such as MV predictions. Therefore, in the same or another embodiment,the disclosed subject matter can be part of a decoder or an encoder.With this understanding, for conciseness, described below is for decoderoperation unless noted otherwise.

FIG. 8 shows a diagram of a current block (810) and neighboringsub-blocks (820, 830, 840). The current block (810) under reconstructioncan be coded using the merge mode, thus, displacements of samples in thecurrent block (810) can be derived from already decoded spatial/temporalneighboring blocks' motion information, including MVs, and without aresidual MV. As described above, the residue MV is zero or is assumed tobe zero in the merge mode, and therefore does not need to be coded.According to aspects of the disclosure, the current block (810) includesan array of motion vector units that, for example, are smaller than thecurrent block (810). The motion vector units are also referred to assub-blocks, and MVs of individual sub-blocks can be different and aredetermined based on respective MVs of the neighboring sub-blocks (820,830, 840). Similarly, the neighboring sub-blocks (820, 830, 840) alsorefer to smaller MV units. In general, a sub-block can include one ormore samples.

The sub-blocks can be of any shape, with or without gaps. In order tosimplify the description, the sub-blocks are assumed to be rectangular.Each sub-block can include K×L samples, for example, luminance sampleswhere K and L are positive integers. In some examples, similarsub-blocks of equal or similar size derive their respective MVs from adedicated main sub-block. For example, in some video processing systemsemploying video decoders, a video is sampled in a YCrCb 4:2:0 samplingstructure with luminance samples Y in a luma plane and correspondingchrominance samples Cr and Cb in respective chroma planes. Thechrominance samples Cr and Cb are subsampled. Accordingly, the spatiallycorresponding sub-blocks in the chroma planes can derive the MVs fromthe luminance sub-block, i.e., the dedicated main sub-block.

In another example, the dedicated main sub-block, also referred to as aG sub-block, can include the green (G) samples of a picture using a RGBcolor space, and sub-blocks including the red (R) and blue (B) samplesare handled in the respective R and B color planes. Accordingly, thespatially corresponding sub-blocks in the R and B color planes canderive the MVs from the G sub-blocks. In order to simplify thedescription, the description is given to a dedicated main sub-block in asingle plane, such as a luma plane, a specific chroma plane, a specificcolor plane, and the like. In the same or another embodiment, motioninformation, such as MVs, of other planes may be predicted only fromcoded motion information related to the single plane, even if the videobitstream contains information related to multiple color planes. In thesame or another embodiment, motion information for certain color planesmay be derived from motion information associated with another colorplane.

In the same or another embodiment, a sub-block can have zero, one, ormore MVs. In the case of a single prediction (such as in P-pictures inMPEG-2), a single MV can be used in the sub-block. In the case ofbi-prediction (such as in direct mode of B pictures in MPEG-2), a twoMVs can be used in the sub-block, one for each prediction direction (aforward prediction and a backward prediction). In certain multipleprediction coding cases, more than two MVs can be used in the sub-block.When a sub-block is not predicted, zero MVs are associated with thesub-block. In order to simplify the description below, described arecases where a sub-block has a single MV associated with the sub-block.The description can be suitably adapted to cases that involve two ormore MVs in the sub-block.

Referring to FIG. 8, each sub-block can include K×L samples. As notedabove, K and L can be positive integer numbers. In one example, K=L=4,such that each sub-block has 4×4 samples. The sub-blocks in the currentblock (810) may have different MVs. In another example, K=L=1, such thateach sub-block has a single sample, and each sample in the current block(810) may have a different MV.

The term “available” or “availability” is introduced below. Certainneighboring samples/sub-blocks or metadata of other prediction entities(such as MVs) may not be “available” for prediction depending on, forexample, a spatial position of the neighboring samples/sub-blocks in apicture. Referring to FIG. 8, when the current block (810) underreconstruction is located at the top (in Y dimension) and in the middle(in X dimension) of a picture (not shown), MVs associated with thesurrounding sub-blocks A(0, 0)-A(0, N+M) have not been previouslyreconstructed or decoded because there is no sub-block data above thepicture boundary. Accordingly, the surrounding sub-blocks A(0, 0)-A(0,N+M) are unavailable. On the other hand, the surrounding sub-blocksL(M+1, 0) and L(M, 0) are available because the current block (810) isin the middle (in X dimension) of the picture, and there can be MVsassociated with one or more sub-blocks to the left of the current block(810). In some embodiments, a bitstream or a video bitstream structureincludes the bitstream partitioned into slices or tiles, and so forth,and a current block is at a boundary of a picture segment, for example,a slice, an independent tile, and the like. Accordingly, the boundary ofa slice or an independent tile is treated, for the purpose of motioninformation prediction, as a picture boundary. In some embodiments, anMV of a neighboring block/sub-block, such as the surrounding sub-blockL(M+1, 0) in FIG. 8, can be unavailable when the neighboringblock/sub-block is coded in a mode which does not allow for motioncompensation, such as a MPEG-2 Intra macroblock mode, thus theneighboring block/sub-block is unavailable. Note that the neighboringsub-blocks (820, 830, 840) can also be referred to as referencesub-blocks and surrounding sub-blocks.

FIG. 8 shows an example of a MV prediction in accordance with the sameor another embodiment where availability is a factor. The current block(810) can include a plurality of sub-blocks C(1, 1)-C(M,N) with M rowsof sub-blocks horizontally and N columns of sub-blocks vertically. M andN are positive integers.

Referring to FIG. 8, the neighboring sub-blocks (820, 830, 840) areadjacent to the current block (810). The neighboring sub-block A(0, 0)(820) is a top-left neighboring sub-block with respect to the currentblock (810). The neighboring sub-blocks A(0, 1)-A(0, N+M) (830) are theabove neighboring sub-blocks (referred to as the top neighboringsub-blocks in some examples) with respect to the current block (810).The neighboring sub-blocks L(1, 0)-L(M+N, 0) (840) are the leftneighboring sub-blocks with respect to the current block (810).

Referring to the above neighboring sub-block A(0, i) where i is apositive integer including 1, N+M. Here, the first element 0 in theabove neighboring sub-block A(0, i) denotes that a vertical spatialdistance, in units of a vertical size of the sub-blocks C(1, 1)-C(M,N),between the neighboring sub-block (820) and the above neighboringsub-block A(0, i) is zero. The second element i in the above neighboringsub-block A(0, i) denotes the position, in units of a horizontal size ofthe sub-block C(1, 1)-C(M,N), relative to the neighboring sub-block(820). For example, the above neighboring sub-block A(0, 2) is thesecond neighboring sub-block from the neighboring sub-block (820). Asimilar nomenclature is utilized for the Y dimension for the leftneighboring sub-blocks L(1, 0)-L(M+N, 0) (840).

To simplify the description, the sub-blocks shown in FIG. 8, such as thesub-blocks C(1, 1)-C(M,N), are of a uniform size, however, thesub-blocks C(1, 1)-C(M,N) can be of any suitable sizes includingnon-uniform sizes and have any suitable shapes including, non-square, ornon-rectangular shapes.

When one or more of the neighboring sub-blocks (820, 830, 840) is notavailable, there are a number of methods to create MV predictors for therespective one or more of the neighboring sub-blocks (820, 830, 840). Inan example, MVs are created for the respective one or more of theneighboring sub-blocks (820, 830, 840) using the merge mode. In anexample, MV predictors are created for the respective one or more of theneighboring sub-blocks (820, 830, 840) using the residual mode, and MVsfor the respective one or more of the neighboring sub-blocks (820, 830,840) are determined based on the MV predictors and residual MVs for therespective one or more of the neighboring sub-blocks (820, 830, 840).

In the same or another embodiment, an MV or an MV predictor can beinferred to be a zero vector when no MV is available for the MVprediction. The zero vector can be a vector where X and Y components areboth zero when the MV or the MV predictor corresponds to atwo-dimensional (2D) MV. In case of three-dimensional MVs, the MV or theMV predictor includes the 2D zero vector and a reference picturecomponent. For example, the reference picture component can indicate afirst reference picture in a given reference picture list, a referencepicture with a smallest GOP distance to the picture currently underreconstruction, and so forth.

In the same or another embodiment, an MV or an MV predictor can bedetermined using, for example, an MV of a spatially closest availablesub-block. For example, in FIG. 8, when the sub-block A(0, N+M) isunavailable, motion information, such as an MV, of the sub-block A(0,N+M−1) can be used to determine the motion information, such as an MV oran MV predictor, of the sub-block A(0, N+M). In general, motioninformation of a block/sub-block can include any suitable informationassociated with motion prediction/compensation for the block/sub-block.In some examples, the motion information can include an MV, an MVpredictor, a residual MV, and the like for the block/sub-block. In someexamples, such as in the residual mode, the MV predictor for theblock/sub-block and the residual MV for the block/sub-block can becombined to determine the MV for the block/sub-block.

In another example in FIG. 8, when the sub-block A(0, N+1) isunavailable, motion information, such as an MV, of the sub-block A(0, N)can be used to determine the motion information, such as an MV or an MVpredictor, of the sub-block A(0, N+1). The selection of the spatiallyclosest available sub-block can take many different options. Forexample, when both the sub-block to the left and the sub-block above areavailable, preference can be given to the sub-block to the left. As analternative, preference can be given to the sub-block above instead ofto the sub-block to the left. A person skilled in the art can readilydevise various other similar preference mechanisms.

Both methods described above and any other suitable methods can be usedin a same picture. For example, when decoding is performed in the scanorder, the top-left sub-block in a picture does not have an MV predictorbecause the top-left sub-block in the picture is the first sub-block tobe decoded in the picture. As a result, a spatially closest availablesub-block is not applicable, thus, an MV predictor can be inferred to bea zero vector. For a sub-block elsewhere in the picture, an MV predictorof the sub-block can be determined using an MV of a spatially closestavailable sub-block.

FIG. 9 shows an example of a MV prediction in accordance with the sameor another embodiment. In various embodiments, the MV prediction canalso be referred to as an MV prediction method, an MV predictiontechnique, or the like. The current block (810) and the neighboringsub-blocks (820, 830, and 840) are identical to those shown in FIG. 8.The current block (810) includes one or more columns of the sub-blocksC(1, 1)-C(M,N), referred to as one or more sub-block columns. Accordingto aspects of the disclosure, MV predictors for a sub-block column canbe predicted from a MV of one of the top neighboring sub-blocks (830)where the one of the top neighboring sub-blocks (830) is in the samecolumn as the sub-block column. In an example, the sub-blocks C(1, 1),C(2, 1), . . . , and C(M, 1) form a first sub-block column, and MVpredictors for the first sub-block column can be predicted using the MVof the top neighboring sub-block A(0, 1), as indicated by an arrow 901.The MV of the top neighboring sub-block A(0, 1) may be available or bepredicted as described above. A person skilled in the art can readilyunderstand that a similar technique can be applied to other columns,such as a second sub-block column including the sub-blocks C(1, 2), C(2,2), . . . , and C(M, 2). MV predictors for the second sub-block columncan be predicted from a MV of the top neighboring sub-block A(0, 2), asindicated by an arrow (902). The MV prediction described in FIG. 9 isreferred to as a vertical prediction method or a vertical prediction.

In the same or another embodiment, the MV of the top neighboringsub-block A(0, 1) is used unmodified as a MV predictor for the firstsub-block column.

The MV prediction described above can offer compression advantages andbitrate savings as MV predictors of a sub-block column can be predictedfrom an already decoded or otherwise readily usable MV, and thereforemay not need to be coded to enable motion compensated prediction.

In some embodiments, the use of vertical prediction described above canbe signaled in a video bitstream, for example, by one or more syntaxelements located in a suitable header associated with the current block(810). For example, the header can include sequence and pictureparameter set, a slice header, a macroblock header, a block header, aCoding Unit (CU) header, and so forth. The signaling can be performedusing any suitable form employed in a video coding technology orstandard, including, for example, fixed or variable length codewords,entropy coded by techniques such as variable length coding, run-lengthcoding, arithmetic coding, Context-Adaptive Binary Arithmetic Coding(CABAC), and so forth.

Compared to previously known techniques, the disclosed motion vectorprediction technique can offer compression advantages and bitratesavings as one or more motion vector predictors of sub-blocks arrangedin a column (such as C(1, 1), C(2, 1), . . . , C(M, 1)) can be predictedfrom an already decoded or otherwise readily usable motion vector, suchas of the top neighboring sub-block A(0, 1), and therefore may not needto be coded to enable motion compensated prediction. Use of the motionvector prediction technique may need to be signaled as described above.To balance signaling overhead and potential or truly realized bitratesavings (ideally to the point where bitrate savings are maximized), inaddition to an effective coding of the signaling information by, forexample, one or more of the techniques mentioned above, it can beadvantageous to signal the use of the vertical prediction for more thanone sub-block columns.

According to aspects of the disclosure, MV predictors for a plurality ofsub-block columns in the current block (810) can be predicted bycorresponding MVs of the respective top neighboring sub-blocks (830).Referring to FIG. 9, the current block (810) includes N sub-blockcolumns. In an example, the Nth sub-block column includes the sub-blocksC(1, N), C(2, N), and C(M,N). The MV prediction for the first, thesecond, . . . , and the Nth sub-block columns is shown by arrows901-90N, respectively. In an example, the plurality of sub-block columnscan include all the sub-block columns in the current block (810). In anexample, the plurality of sub-block columns can include a subset of thesub-block columns in the current block (810). A person skilled in theart can readily devise the appropriate subset, such as, the left/righthalf of the sub-block columns, and so forth.

Using the MVs of the top neighboring sub-blocks A(0, 1)-A(0, N) abovethe current block (810) as described above may require storing the MVsin, for example, a motion vector line buffer that operates at asub-block granularity. In the same or another embodiment, additionalmemory space is allocated to store the MVs in addition to memoryrequirements of an encoder or decoder not using the disclosed subjectmatter. Alternatively, the MVs of the top neighboring sub-blocks A(0,1)-A(0, N) are not stored, and the additional memory space is not used.Therefore, the unavailable MVs of the top neighboring sub-blocks A(0,1)-A(0, N) may be derived from available sub-block motion vectors usingany suitable technique, including the techniques described above.

In an embodiment, all the sub-block columns in the current block (810)are predicted using the vertical prediction described above, thus,minimizing signaling overhead. For example, experiments have shown that,for at least certain block and sub-block sizes and certain videocontent, bit rate savings can be achieved.

The application of the disclosed subject matter is not restricted toscenarios where the sub-blocks are of a uniform size. FIG. 10 shows twoexamples where a size of sub-blocks of a current block (1010) underreconstruction is different from a size of a top neighboring sub-block,such as A(0, 1), A(0, 3), and A(0, 4). The current block (1010) isdivided into three sub-block columns (1021-1023). The sub-block column(1021) includes sub-blocks C(1, 1), C(2, 1), C(3, 1), and C(4, 1), andthe sub-block column (1022) includes sub-blocks C(1, 2), C(2, 2), C(3,2), and C(4, 2). The sub-blocks in the sub-block columns (1021-1022) aresquare sub-blocks with, for example, 4×4 luma samples (not depicted).The sub-block column (1023) includes non-square sub-blocks C(1, 3), C(2,3), C(3, 3), and C(4, 3) having a width and a height. The width is twicethat of the height, for example, each of the non-square sub-blocksincludes 8×4 luma samples (not depicted). Similarly, the top neighboringsub-blocks A(0, 1), A(0, 3), and A(0, 4) are not of the same size. Forexample, the top neighboring sub-block A(0, 1) is a square sub-block of,for example, 8×8 luma samples, whereas the top neighboring sub-blocksA(0, 3) and A(0, 4) are square sub-blocks of 4×4 luma samples.

In the same or another embodiment, the MV predictors for the sub-blockcolumns (1021, 1022) can be predicted from a MV of the top neighboringsub-block A(0, 1), as shown by a forked line (1001). In the same oranother embodiment, MV predictors of more than two sub-block columns canbe predicted from a top neighboring sub-block's MV.

MV predictors of the sub-block column (1023) can be derived using anysuitable vertical predictions. In an example, the MV predictors of thesub-block column (1023) can be predicted from the top neighboringsub-block A(0, 3) that is above the sub-block column (1023), as shown byan arrow (1003). In another example, the MV predictors of the sub-blockcolumn (1023) can be predicted from the top neighboring sub-block A(0,4) that is also above the sub-block column (1023) (not predicted). Inanother example, the MV predictors of the sub-block column (1023) can bepredicted from a suitable combination of the MVs of the top neighboringsub-blocks A(0, 3) and A(0, 4). Suitable combinations can include, forexample, a smaller MV of the MVs (measured in any suitable dimension ora combination of dimensions and suitably weighted, for example, moreweight can be given to a spatial dimension than to a reference picturedimension), an average of the MVs, a linear interpolation of the MVs,any other suitable interpolation of the MVs, and so forth.

MVs from more than two top neighboring sub-blocks can be used forpredicting MV predictors of a sub-block column, by suitably combiningthe MVs. Suitable combinations can include any of the suitablecombination described above as well as a median of the MVs.

Referring to FIG. 8, according to aspects of the disclosure, MVpredictors for a plurality of sub-blocks along a prediction directioncan be predicted from a MV of one of the neighboring sub-blocks (820,830, 840) where the one of the neighboring sub-blocks (820, 830, 840) isalong the same prediction direction as the plurality of sub-blocks, asdescribed in FIGS. 9 and 10 above and in FIGS. 11-16 below. In someexamples, the one of the neighboring sub-blocks (820, 830, 840) isadjacent to the plurality of sub-blocks.

The vertical prediction including various embodiments/adaptionsdescribed above in FIGS. 9 and 10 can be suitably adapted to otherdirections, such as a horizontal prediction (or a horizontal predictionmethod) as shown in FIG. 11. FIG. 11 shows an example of a MV predictionin accordance with the same or another embodiment. The current block(810) and the neighboring sub-blocks (820, 830, and 840) are identicalto those shown in FIG. 8. The current block (810) includes one or morerows of the sub-blocks C(1, 1)-C(M,N), referred to as one or moresub-block rows. According to aspects of the disclosure, MV predictorsfor a sub-block row can be predicted from a MV of one of the leftneighboring sub-blocks (840) where the one of the left neighboringsub-blocks (840) is to the left of the sub-block column. In an example,the sub-blocks C(1, 1), C(1, 2), . . . , and C(1, N) form a firstsub-block row, and MV predictors for the first sub-block row can bepredicted using the MV of the left neighboring sub-block L(1, 0), asindicated by an arrow (1101). Additional descriptions of othervariations and embodiments are similar to those of the verticalprediction shown in FIGS. 9-10 and are omitted for purposes of clarity.

FIG. 12A shows an example of a MV prediction in accordance with the sameor another embodiment. For purposes of clarity, a current block (1210)includes 4×4 sub-blocks C(1, 1)-C(4, 4). Neighboring sub-blocks includeA(0, 0)-A(0, 4), and L(1, 0)-L(4, 0). According to aspects of thedisclosure, MV predictors of sub-blocks along a top-left diagonaldirection (also referred to as a diagonal prediction direction), such asindicated by an arrow (1204), can be predicted from a MV of one of theneighboring sub-blocks where the one of the neighboring sub-blocks is tothe top-left of the sub-blocks. In an example, the sub-blocks C(1, 1),C(2, 2), C(3, 3), and C(4, 4) form a first sub-block group, and MVpredictors for the first sub-block group can be predicted using the MVof the neighboring sub-block A(0, 0), as indicated by the arrow (1204).Similarly, MV predictors of other sub-block groups can be predictedusing MVs of their respective neighboring sub-blocks, as indicated bythe arrows (1201-1203) and (1205-1207). The MV prediction described inFIG. 12A is referred to as a diagonal prediction (or a diagonalprediction method) with a diagonal prediction direction.

Additional descriptions of other variations and embodiments are similarto those of the vertical prediction shown in FIGS. 9-10 and are omittedfor purposes of clarity. As an example of the other variations andembodiments, FIG. 12B shows an example where a size of sub-blocks of acurrent block (1220) is different from a size of a neighboringsub-block, such as A(0, 0)-A(0, 4) and L(1, 0)-L(4, 0). The currentblock (1220) is divided into four square sub-blocks C(1, 1), C(1, 2),C(2, 1), and C(2, 2) with, for example, 8×8 luma samples (not depicted).The neighboring sub-blocks A(0, 0)-A(0, 4) and L(1, 0)-L(4, 0) aresquare sub-blocks with, for example, 4×4 luma samples. In an embodiment,MV predictors of a first sub-block group including C(1, 1) and C(2, 2)along the top-left diagonal direction indicated by an arrow (1212), canbe predicted from a MV of the neighboring sub-block A(0, 0).

FIG. 13 shows an example of a MV prediction in accordance with the sameor another embodiment. For purposes of clarity, a current block (1310)includes 4×4 sub-blocks C(1, 1)-C(4, 4). Top neighboring sub-blocksinclude A(0, 0)-A(0, 8). According to aspects of the disclosure, MVpredictors of sub-blocks along a top-right diagonal direction (alsoreferred to as a top-right prediction direction), such as indicated byan arrow (1304), can be predicted from a MV of one of the topneighboring sub-blocks where the one of the top neighboring sub-blocksis to the top-right of the sub-blocks. In an example, the sub-blocksC(1, 4), C(2, 3), C(3, 2), and C(4, 1) form a first sub-block group, andMV predictors for the first sub-block group can be predicted using a MVof the neighboring sub-block A(0, 5), as indicated by the arrow (1304).Similarly, MV predictors of other sub-block groups can be predictedusing MVs of the respective top neighboring sub-blocks, as indicated byarrows (1301-1303), and (1305-1307). Additional descriptions of othervariations and embodiments are similar to those of the verticalprediction shown in FIGS. 9-10 and are omitted for purposes of clarity.The MV prediction described in FIG. 13 is referred to as a top-rightdiagonal prediction (or a top-right diagonal prediction method) with thetop-right diagonal prediction direction.

FIG. 14 shows an example of a MV prediction in accordance with the sameor another embodiment. For purposes of clarity, a current block (1410)includes 4×4 sub-blocks C(1, 1)-C(4, 4). Left neighboring sub-blocksinclude L(1, 0)-L(8, 0). According to aspects of the disclosure, MVpredictors of sub-blocks along a bottom-left diagonal direction, such asindicated by an arrow (1404), can be predicted from a MV of one of theleft neighboring sub-blocks where the one of the left neighboringsub-blocks is to the bottom-left of the sub-blocks. In an example, thesub-blocks C(1, 4), C(2, 3), C(3, 2), and C(4, 1) form a first sub-blockgroup, and MV predictors for the first sub-block group can be predictedusing the MV of the left neighboring sub-block L(5, 0), as indicated bythe arrow (1404). Similarly, MV predictors of other sub-block groups canbe predicted using MVs of the respective left neighboring sub-blocks, asindicated by arrows (1401-1403) and (1405-1407). Additional descriptionsof other variations and embodiments are similar to those of the verticalprediction shown in FIGS. 9-10 and are omitted for purposes of clarity.The MV prediction described in FIG. 14 is referred to as a bottom-leftdiagonal prediction (or a bottom-left diagonal prediction method) withthe bottom-left diagonal prediction direction.

Note that in the various predictions described above, each sub-block ina current block under reconstruction can correspond to a specificneighboring sub-block. For example, in FIG. 12A, the sub-block C(4, 4)corresponds to the neighboring sub-block A(0, 0), thus, the MV predictorfor the sub-block C(4, 4) is predicted from motion information of theneighboring sub-block A(0, 0).

In addition to predicting MV predictors for a plurality of sub-blocks ina row, in a column, or along a certain diagonal direction, in a currentblock using neighboring sub-blocks of the current block, MV predictorsfor a plurality of sub-blocks along any suitable prediction directioncan be predicted using one or more neighboring sub-blocks, as shown inFIGS. 15-16.

To simplify the description, FIG. 15 shows a current block underreconstruction (1510) that includes 4×4 sub-blocks C(1, 1)-C(4, 4) andneighboring sub-blocks A(0, 0)-A(0, 4) and L(1, 0)-L(4, 0). Positions ofthe sub-blocks C(1, 1)-C(4, 4) and the neighboring sub-blocks A(0,0)-A(0, 4) and L(1, 0)-L(4, 0) can be represented by respective samplesin the sub-blocks C(1, 1)-C(4, 4) and the neighboring sub-blocks A(0,0)-A(0, 4) and L(1, 0)-L(4, 0). In general, positions of any suitablesamples in a block or a sub-block can be used to represent a position ofthe block or the sub-block, such as a top-left corner, a centerposition, and the like of the block/sub-block. In some embodiments, suchas shown in FIG. 15, a top-left sample of a sub-block is used torepresent a position of the sub-block. As described above, any suitableprediction direction can be used in predicting MV predictors for aplurality of sub-blocks in the current block (1510). Referring to FIG.15, a prediction direction is indicated by an arrow (1501). In anembodiment, an MV predictor of a sub-block is predicted by extending theprediction direction from a position of the sub-block to be predicted tofind a corresponding neighboring sub-block. For example, in FIG. 15, anMV predictor of the sub-block C(3, 3) is predicted by A(0, 2) because aposition of the neighboring sub-block A(0, 2), represented by thetop-left sample of the neighboring sub-block A(0, 2), lies in theextended prediction direction.

Referring to FIG. 15, a horizontal reference line (1530) goes throughpositions P1-P5 of the neighboring sub-blocks A(0, 0)-A(0, 4),respectively. A vertical reference line (1540) goes through positions P1and P6-P9 of the neighboring sub-blocks A(0, 0) and L(1, 0)-L(4, 0). Insome embodiments, an extended prediction direction intersects with thehorizontal reference line (1530) or the vertical reference line (1540)at a location that is not a position of a neighboring sub-block, thus,the location is referred to as a non-integer location. In otherembodiments, when an extended prediction direction and the horizontalreference line (1530) or the vertical reference line (1540) intersect ata position of a neighboring sub-block, such as one of the positionsP1-P9, the corresponding neighboring sub-block can be used to predictmotion information of the sub-block. For example, techniques related toFIGS. 9 and 11-14 use integer positions to perform MV prediction.

For a non-integer location, the MV for the intersected non-integerlocation can be derived from MVs for neighboring sub-blocks that areadjacent to the non-integer location. FIG. 16 shows neighboringsub-blocks A(0, L−1)-A(0, L+2) of a current block under reconstruction(not shown). A prediction direction indicated by an arrow (1601)intersects a horizontal reference line (1630) at a location (1602) thatis a non-integer location. As described above, motion informationassociated with the intersected non-integer location or the location(1602), can be derived from motion information associated withneighboring sub-blocks that are adjacent to the location. In someembodiments, the motion information associated with the location (1602)can be derived from a weighted average of the motion informationassociated with the respective neighboring sub-blocks, such as theneighboring sub-blocks A(0, L) and A(0, L+1).

In an embodiment, a weight associated with the respective neighboringsub-block is inversely proportional to a distance between the location(1602) and a position of the neighboring sub-block. Referring to FIG.16, weights w1 and w2 correspond to the neighboring sub-blocks A(0, L)and A(0, L+1), a distance d1 is a distance between the location (1602)and a position P2 of the neighboring sub-block A(0, L), and a distanced2 is a distance between the location (1602) and a position P3 of theneighboring sub-block A(0, L+1). Accordingly, a ratio of w1/w2 isinversely proportional to a ratio of d1/d2, for example, w1/w2=d2/d1.Therefore, the motion information associated with the location (1602)can be equal to a weighted summation of the respective motioninformation associated with the neighboring sub-blocks A(0, L) and A(0,L+1).

In another embodiment, motion information from additional neighboringsub-blocks, such as the neighboring sub-blocks A(0, L−1) and A(0, L+1),is also included but larger weights are given to the closest neighboringsub-blocks A(0, L) and A(0, L+1). In various examples, a number ofneighboring sub-blocks that contribute to the motion informationassociated with the location (1602) can be any suitable positiveintegers, such as 2, 4, or the like.

In an embodiment, the motion information associated with the closestneighboring sub-block is used. Referring to FIG. 16, the location (1602)is closer to A(0, L+1) than to A(0, L) (d2<d1), thus the motioninformation of A(0, L+1) is chosen to predict MV predictors forrespective sub-blocks along the prediction direction indicated by thearrow 1601 in the current block.

In some embodiments, a neighboring sub-block is chosen according to aquantized location of the location (1602). A quantization method isdefined to locate the quantized location so that after using thequantization method, the quantized location falls into a representativeposition of a respective neighboring sub-block. For example, a flooringoperation (choosing the largest integer that is smaller or equal to acurrent value) is chosen as the quantization method. After the flooringoperation, the location (1602) shares the same position with P2, thusthe motion information of A(0, L) is chosen to predict MV predictors forrespective sub-blocks in the current block. In another example, aceiling operation (choosing the smallest integer that is larger or equalto a current value) is chosen as the quantization method. After theceiling operation, the location (1602) shares the same position with P3,thus the motion information of A(0, L+1) is chosen to predict MVpredictors for respective sub-blocks in the current block. In someexamples, the MV predictions described in FIGS. 9 and 11-14 are specialexamples of the MV prediction described in FIGS. 15 and 16.

As described above in reference to FIGS. 9-16, MV predictors of aplurality of sub-blocks (e.g., in a single row, column, or diagonal) canbe predicted from an already decoded or otherwise readily usable MV, andtherefore may not need to be coded to enable motion compensatedprediction. Further, in some examples, MV predictors of all sub-blocksin a current block under reconstruction can be predicted from aplurality of already decoded or otherwise readily usable MVs, andtherefore may not need to be coded to enable motion compensatedprediction. Therefore, the MV prediction methods described above canoffer compression advantages and bitrate savings.

According to aspects of the disclosure, the techniques described abovecan be suitably combined to predict MV predictors of respectivesub-blocks in a current block. In various embodiments, first MVpredictors of the sub-blocks can be predicted using a MV predictionmethod, for example, the vertical prediction, second MV predictors ofthe sub-blocks can be predicted using another MV prediction method, forexample, the horizontal prediction, the first MV predictors and thecorresponding second MV predictors of the sub-blocks can be suitablycombined to generate combined MV predictors of the sub-blocks.

In an example, first MV predictors of the sub-blocks can be predictedusing the top-right diagonal prediction, second MV predictors of thesub-blocks can be predicted using the bottom-left diagonal prediction,the first MV predictors and the corresponding second MV predictors ofthe sub-blocks can be suitably combined to generate combined MVpredictors of the sub-blocks.

In various examples, the combined MV predictors are obtained using aweighted combination of the first and second MV predictors, thus, thecombined MV predictors for the sub-blocks are predicted by both top andthe left neighboring sub-blocks associated with the current block. Insome examples, combined MV predictors can be obtained using a weightedcombination of respective MV predictors from various diagonalpredictions, such as the top-right diagonal prediction and thebottom-left diagonal prediction. Any suitable weights can be applied tothe sub-blocks. In some examples, different weights can be applied tothe sub-blocks. In one embodiment, a weight is related to a distancebetween the sub-block and the respective neighboring sub-block used topredict the motion information of the sub-block. For example, when theneighboring sub-block is closer to the sub-block, a higher weight isapplied to the MV predictor associated with the neighboring sub-block.

In some examples, the use of a prediction method described above can besignaled in a video bitstream, for example, by a codeword, one or moresyntax elements, and the like. For example, the codeword or the one ormore syntax elements can indicate the prediction method and informationassociated with the prediction method, such as the vertical prediction,the horizontal prediction, the diagonal prediction, and the like.

As described above, the application of the disclosed subject matter isnot restricted to scenarios where sub-blocks are of a uniform size.FIGS. 10 and 12B show various examples where a size of sub-blocks of acurrent block is different from a size of a neighboring sub-block. Ingeneral, other MV predictions described above, such as in FIGS. 11,13-16 can be suitably adapted to be applicable to various scenarioswhere a size of sub-blocks of a current block is different from a sizeof a neighboring sub-block.

In some embodiments, MVs of sub-blocks in a current block are obtainedbased on respective MV predictors of the sub-blocks. In some examples,the MVs can be obtained by refining the respective MV predictors usingdecoder side motion vector derivation methods, such as templatematching, bilateral matching, and the like. The refined MVs for thesub-blocks are used in motion compensation. In various examples, thesame or similar MV prediction and refinement can be performed at bothencoder and decoder side, thus, no additional information is needed tobe signaled in the video bitstream.

In some embodiments, such as in the residual or regular mode, MVs ofsub-blocks in a current block under reconstruction are obtained based onrespective MV predictors of the sub-blocks and corresponding residualMVs that are coded.

In general, sub-block based merge candidates associated with the MVprediction methods described above, also referred to as sub-blockcandidates, can be integrated into a merge candidate list that includesvarious existing merge candidates, such as block-based merge candidates,affine merge candidates, and the like. In some examples, one or more ofthe sub-block candidates can replace one or more of the various existingmerge candidates.

Referring to FIG. 8, in a first example, when the vertical predictionand the horizontal prediction are considered, a merge candidate list caninclude A(0, N+1), the vertical prediction, A(0, 0), the horizontalprediction, L(M+1, 0), and the like where A(0, N+1), A(0, 0), and L(M+1,0) represent block-based merge candidates. In a second example, when thevertical prediction, the horizontal prediction, and the diagonalprediction are considered, a merge candidate list can include A(0, N+1),the vertical prediction, the diagonal prediction, the horizontalprediction, L(M+1, 0), and the like. In a third example, a mergecandidate list can include the right-down diagonal prediction, thevertical prediction, the diagonal prediction, the horizontal prediction,the left-up diagonal prediction, and the like. In a fourth example, amerge candidate list can include A(0, N+1), the right-down diagonalprediction, the vertical prediction, A(0, 0), the diagonal prediction,the horizontal prediction, L(M+1, 0), the left-up diagonal prediction,and the like. In various embodiments, an order of existing mergecandidates and sub-block candidates in a candidate list can be changed.

When all sub-blocks in a current block under reconstruction share thesame motion information, a sub-block based MV prediction becomes a blockbased MV prediction. When the motion information represented by thesub-block candidate is already represented by a certain block-basedmerge candidate, the sub-block candidate duplicates the block-basedmerge candidate, and the duplicated sub-block candidate can be removedfrom the merge candidate list.

FIG. 17 shows a flow chart outlining a process (1700) according to someembodiments of the disclosure. The process (1700) is used in a mergemode to generate a prediction block for a current block. In variousembodiments, the process (1700) is executed by processing circuitry,such as the processing circuitry in the terminal devices (210, 220, 230and 240), the processing circuitry that performs functions of the videoencoder (303), the processing circuitry that performs functions of thevideo decoder (310), the processing circuitry that performs functions ofthe video decoder (410), the processing circuitry that performsfunctions of the motion compensation prediction module (453), theprocessing circuitry that performs functions of the video encoder (503),the processing circuitry that performs functions of the predictor (535),the processing circuitry that performs functions of the inter encoder(630), the processing circuitry that performs functions of the interdecoder (780), and the like. The process starts at (S1701) and proceedsto (S1710).

At (S1710), inter prediction information for the current block isreceived or otherwise acquired. For example, the inter predictioninformation is indicative of a merge mode. Thus, the processingcircuitry constructs a merge candidate list for the merge mode for interprediction. In an example, the candidate list includes sub-blockcandidates determined using the vertical prediction, or the like asdescribed above.

At (S1720), the processing circuitry determines a certain MV predictionmethod to predict the MV predictors of the current block. In someembodiments, the certain MV prediction method can be the verticalprediction, the horizontal prediction, the diagonal prediction, or MVprediction along any suitable prediction direction as described above.In some examples, the certain MV prediction method can utilize aweighted combination of MV predictors obtained from multiple MVpredictions, such as the vertical prediction and the horizontalprediction.

At (S1730), the processing circuitry selects neighboring MVs that areassociated with neighboring sub-blocks of the current block based on theMV prediction method. For example, referring to FIG. 9, when thevertical prediction is selected at (S1720) for the current block (810),the MVs of the neighboring sub-blocks A(0, 1) to A(0, N) are selected topredict the MV predictors for the sub-block columns (901-90N),respectively.

At (S1740), the processing circuitry determines whether the neighboringsub-blocks are available, as described above. When one or more of theneighboring motion vectors are unavailable, the process (1700) proceedsto (S1750). When the neighboring sub-blocks are available, the process(1700) proceeds to (S1760).

At (S1750), the processing circuitry determines neighboring MVs for theone or more unavailable neighboring sub-blocks, as described above. Theprocess (1700) then proceeds to (S1760).

At (S1760), the processing circuitry determines MVs for the sub-blocksin the current block based on the respective neighboring MVs, such asdescribed with reference to FIGS. 9-16. Then the process proceeds to(S1799) and terminates.

In some embodiments, the process (1700) can include other steps. In anexample, the process (1700) can generate the sub-blocks according to theMVs for the sub-blocks. Further, the process (1700) can combine thesub-blocks to form a prediction block for the block

The techniques for motion vector prediction with sub-block granularity,described above, can be implemented as computer software usingcomputer-readable instructions and physically stored in one or morecomputer-readable media. For example, FIG. 18 shows a computer system1800 suitable for implementing certain embodiments of the disclosedsubject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 18 for computer system (1800) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1800).

Computer system (1800) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1801), mouse (1802), trackpad (1803), touchscreen (1810), data-glove (not shown), joystick (1805), microphone(1806), scanner (1807), camera (1808).

Computer system (1800) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1810), data-glove (not shown), or joystick (1805), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1809), headphones(not depicted)), visual output devices (such as screens (1810) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1800) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1820) with CD/DVD or the like media (1821), thumb-drive (1822),removable hard drive or solid state drive (1823), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1800) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1849) (such as, for example USB ports of thecomputer system (1800)); others are commonly integrated into the core ofthe computer system (1800) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1800) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1840) of thecomputer system (1800).

The core (1840) can include one or more Central Processing Units (CPU)(1841), Graphics Processing Units (GPU) (1842), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1843), hardware accelerators for certain tasks (1844), and so forth.These devices, along with Read-only memory (ROM) (1845), Random-accessmemory (1846), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1847), may be connectedthrough a system bus (1848). In some computer systems, the system bus(1848) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1848),or through a peripheral bus (1849). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1841), GPUs (1842), FPGAs (1843), and accelerators (1844) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1845) or RAM (1846). Transitional data can be also be stored in RAM(1846), whereas permanent data can be stored for example, in theinternal mass storage (1847). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1841), GPU (1842), massstorage (1847), ROM (1845), RAM (1846), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1800), and specifically the core (1840) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1840) that are of non-transitorynature, such as core-internal mass storage (1847) or ROM (1845). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1840). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1840) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1846) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1844)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

Appendix A: Acronyms

-   MV: Motion Vector-   HEVC: High Efficiency Video Coding-   SEI: Supplementary Enhancement Information-   VUI: Video Usability Information-   GOPs: Groups of Pictures-   TUs: Transform Units,-   PUs: Prediction Units-   CTUs: Coding Tree Units-   CTBs: Coding Tree Blocks-   PBs: Prediction Blocks-   HRD: Hypothetical Reference Decoder-   SNR: Signal Noise Ratio-   CPUs: Central Processing Units-   GPUs: Graphics Processing Units-   CRT: Cathode Ray Tube-   LCD: Liquid-Crystal Display-   OLED: Organic Light-Emitting Diode-   CD: Compact Disc-   DVD: Digital Video Disc-   ROM: Read-Only Memory-   RAM: Random Access Memory-   ASIC: Application-Specific Integrated Circuit-   PLD: Programmable Logic Device-   LAN: Local Area Network-   GSM: Global System for Mobile communications-   LTE: Long-Term Evolution-   CANBus: Controller Area Network Bus-   USB: Universal Serial Bus-   PCI: Peripheral Component Interconnect-   FPGA: Field Programmable Gate Areas-   SSD: solid-state drive-   IC: Integrated Circuit-   CU: Coding Unit

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method for video decoding in a decoder,comprising: selecting, by processing circuitry of the decoder, aneighboring sub-block outside a current block for a current sub-block inthe current block based on a prediction direction that indicates aspatial relationship between the current sub-block and the selectedneighboring sub-block, the selected neighboring sub-block and thecurrent block being in a coded picture from a coded bitstream, and arepresentative position of the current sub-block being on a referenceline extended along the prediction direction from a reference positionthat is on or adjacent to a representative position of the selectedneighboring sub-block; determining, by the processing circuitry of thedecoder, a reference motion vector corresponding to the referenceposition based on a motion vector for coding the selected neighboringsub-block; determining, by the processing circuitry of the decoder, amotion vector predictor for the current sub-block based on the referencemotion vector; and decoding the current sub-block for output usinginter-picture prediction performed based on the motion vector predictor.2. The method of claim 1, wherein the selected neighboring sub-block andthe current sub-block are in a same column of the coded picture, and theselected neighboring sub-block is a top neighbor of the current block.3. The method of claim 1, wherein the selected neighboring sub-block andthe current sub-block are in a same row of the coded picture, and theselected neighboring sub-block is a left neighbor of the current block.4. The method of claim 1, wherein a motion vector predictor for eachremaining sub-block included in the current block is determined from amotion vector of a respective neighboring sub-block that is selectedbased on the prediction direction.
 5. The method of claim 1, furthercomprising: decoding a codeword from the coded bitstream, the codewordindicating the prediction direction.
 6. The method of claim 1, furthercomprising: decoding, from the coded bitstream, a residual motion vectorfor the current sub-block; and combining the motion vector predictorwith the residual motion vector to derive a current motion vector forthe current sub-block.
 7. The method of claim 1, further comprising:decoding at least one syntax element from the coded bitstream, the atleast one syntax element indicating the prediction direction.
 8. Themethod of claim 1, further comprising: deriving a motion vector for thecurrent sub-block based on refining the motion vector predictor usingone of template matching and bilateral matching.
 9. The method of claim1, further comprising: selecting another neighboring sub-block in thecoded picture outside the current block for the current sub-block basedon the prediction direction, the reference position being adjacent toanother representative position of the other selected neighboringsub-block and the representative position of the selected neighboringsub-block; and determining the reference motion vector corresponding tothe reference position based on the motion vector for coding theselected neighboring sub-block and another motion vector for coding theother selected neighboring sub-block.
 10. The method of claim 9, whereinthe determining the reference motion vector corresponding to thereference position is performed using a weighted combination of themotion vector for coding the selected neighboring sub-block and theother motion vector for coding the other selected neighboring sub-block.11. A decoder device, comprising processing circuitry configured to:select, a neighboring sub-block outside a current block for a currentsub-block in the current block based on a prediction direction thatindicates a spatial relationship between the current sub-block and theselected neighboring sub-block, the selected neighboring sub-block andthe current block being in a coded picture from a coded bitstream, and arepresentative position of the current sub-block being on a referenceline extended along the prediction direction from a reference positionthat is on or adjacent to a representative position of the selectedneighboring sub-block; determine a reference motion vector correspondingto the reference position based on a motion vector for coding theselected neighboring sub-block; determine a motion vector predictor forthe current sub-block based on the reference motion vector; and decodethe current sub-block for output using inter-picture predictionperformed based on the motion vector predictor.
 12. The decoder deviceof claim 11, wherein the selected neighboring sub-block and the currentsub-block are in a same column of the coded picture, and the selectedneighboring sub-block is a top neighbor of the current block.
 13. Thedecoder device of claim 11, wherein the selected neighboring sub-blockand the current sub-block are in a same row of the coded picture, andthe selected neighboring sub-block is a left neighbor of the currentblock.
 14. The decoder device of claim 11, wherein the processingcircuitry is further configured to: determine a motion vector predictorfor each remaining sub-block included in the current block from a motionvector of a respective neighboring sub-block that is selected based onthe prediction direction.
 15. The decoder device of claim 11, whereinthe processing circuitry configured to: decode a codeword from the codedbitstream, the codeword indicating the prediction direction.
 16. Thedecoder device of claim 11, wherein the processing circuitry is furtherconfigured to: select another neighboring sub-block in the coded pictureoutside the current block for the current sub-block based on theprediction direction, the reference position being adjacent to anotherrepresentative position of the other selected neighboring sub-block andthe representative position of the selected neighboring sub-block; anddetermine the reference motion vector corresponding to the referenceposition based on the motion vector for coding the selected neighboringsub-block and another motion vector for coding the other selectedneighboring sub-block.
 17. The decoder device of claim 16, wherein theprocessing circuitry is further configured to: determine the referencemotion vector corresponding to the reference position using a weightedcombination of the motion vector for coding the selected neighboringsub-block and the other motion vector for coding the other selectedneighboring sub-block.
 18. The decoder device of claim 11, wherein theprocessing circuitry is further configured to: decode, from the codedbitstream, a residual motion vector for the current sub-block; andderive a current motion vector for the current sub-block by combing themotion vector predictor for the current sub-block with the residualmotion vector.
 19. A non-transitory computer-readable storage mediumstoring a program executable by at least one processor to perform:selecting a neighboring sub-block outside a current block for a currentsub-block in the current block based on a prediction direction thatindicates a spatial relationship between the current sub-block and theselected neighboring sub-block, the selected neighboring sub-block andthe current block being in a coded picture from a coded bitstream, and arepresentative position of the current sub-block being on a referenceline extended along the prediction direction from a reference positionthat is on or adjacent to a representative position of the selectedneighboring sub-block; determining a reference motion vectorcorresponding to the reference position based on a motion vector forcoding the selected neighboring sub-block; determining a motion vectorpredictor for the current sub-block based on the reference motionvector; and decoding the current sub-block for output usinginter-picture prediction performed based on the motion vector predictor.20. The method of claim 1, wherein the prediction direction is selectedfrom a group of directions including a vertical prediction direction, ahorizontal prediction direction, and a diagonal prediction direction.21. The non-transitory computer-readable storage medium of claim 19,wherein the prediction direction is selected from a group of directionsincluding a vertical prediction direction, a horizontal predictiondirection, and a diagonal prediction direction.
 22. The decoder deviceof claim 11, wherein the prediction direction is selected from a groupof directions including a vertical prediction direction, a horizontalprediction direction, and a diagonal prediction direction.